In metal machining processes such as cutting and grinding, a metal-working oil agent is used for improving machining efficiency, for preventing abrasion between a workpiece and a tool for machining the workpiece, for prolonging tool life, for removing metal chips, and for other purposes. Such metal metal-working oil agents include an oil-base agent predominantly containing an oil component such as mineral oil, animal and vegetable oil, or synthetic oil, and a water-soluble agent containing an oil component and a surface active compound. From the viewpoints of effective utilization of resources and fire prevention, a water-solubility-imparted agent (i.e., a water-soluble metal-working oil agent) has come to be used more and more in recent years.
In order to satisfy defoaming property and rotting resistance which are essential properties of the water-soluble metal-working oil agent and also to enhance machining efficiency, one proposed solution is incorporation of a compound, such as risinoleic acid polymer amine salt, into a metal-working oil agent (see Patent Document 1). Conventionally, chlorinated paraffin has been incorporated into a metal-working oil agent for the purpose of enhancing machining efficiency. However, since such a halohydrocarbon possibly generates dioxin, which is harmful to the human body, in recent years, a compound such as a sulfur compound or a phosphorus compound is used instead of chlorinated paraffin (see Patent Document 2). Furthermore, in order to attain further enhanced workability, there has been proposed incorporation, into a metal-working oil agent, of a compound such as a condensed risinoleic fatty acid, an ester compound, or an amine (see Patent Document 3).
However, as disclosed in Patent Documents 1 and 3, even in the case of a metal-working oil agent composed of a mixture of a risinoleic acid polycondensation product amine salt and a mineral oil, when a material which is difficult to work; i.e., hard-to-work material, such as titanium alloy, nickel alloy, or cobalt alloy, is subjected to cutting work, the heat generated during the working accumulates in a tool, and such an increased heat load causes problems, including shortening of tool life.
In another case where cutting speed is elevated to enhance productivity, higher heat is generated, and the heat imposes a further load on the tool. Thus, even in the case disclosed in Patent Document 3, where a risinoleic-acid-polycondensed fatty acid and an ester compound are used in combination, sufficient workability may fail to be attained. In the case disclosed in Patent Document 2, use of a sulfur compound or a phosphorus compound may impose a load on the environment.
Therefore, in machining hard-to-work materials, there is demand for further improvement of a metal-working oil agent.